1. Field of the Invention
The present invention relates to an improved method of operating diesel engines equipped with Diesel Particulate Filter (DPF) and Exhaust Gas Recirculation (EGR) systems, to reduce emissions of Particulate Matter (PM), unburned Hydrocarbons (HC) and Oxides of Nitrogen (NOx) from diesel engines. More specifically, the present invention is related to a catalytic DPF system that improves emissions by filtering exhaust, and which regenerates the filter by burning off collected PM therefrom. This invention is further related to a method of reducing NOx through the use of a cooled EGR gas, as well as introduction of water into a diesel engine combustion system. The present invention also relates to an engine anti-wear lubricating composition, and to a method of employing such engine lubricant oil in internal combustion engines, including diesel engines.
2. Description of the Background Art
In efforts to reduce global-warming gas emissions, energy-efficient internal combustion engines, such as Diesel engines, may be advantageously utilized. Diesel engines have also remained popular, due to their fuel efficiency.
One method of increasing energy efficiency of an internal combustion engine is to reduce frictional energy loss by increasing the engine lubrication performance.
However, it is well known that Diesel engines emit particulate matter (PM) and nitrogen oxides (NOx) in their exhaust gases. A problem exists because concurrent reduction of both PM and NOx from diesel engines is difficult, due to a well-known trade-off relationship between the production of these two emission products in the diesel combustion process.
Diesel engine combustion technology has been greatly advanced with the advent of electronic controls and common-rail injection systems. However, it must be recognized that the engine combustion system alone cannot meet future diesel emissions standards, particularly with regard to PM and NOx.
Unexpectedly, it has recently been discovered that advanced diesel engines emit “ultra-fines”; i.e., finely dispersed particulates, in great numbers. Such finely dispersed particles are believed to be toxic to human health. Moreover, it is well-established now that of the known cures, only the DPF technology, when installed in the diesel exhaust system, can effectively reduce PM, and the related ultra-fines, from diesel engines by a high percentage, such as 99.9% (by particle-counts). Therefore, DPF is going to be required, and is expected to be equipped on all diesel engines, both new and old, throughout the world, beginning in the near future.
Catalytic DPF (CDPF) process have been proposed which include a catalyst in either (1) a catalytic trap that is pre-treated on the trap substrate, or as (2) a fuel-borne catalyst (FBC) where a catalytic component is supplied continuously with fuel, by a metering device connected to a separate additive tank.
Examples of patents relating to CDPF processes include U.S. Pat. No. 6,248,689, “Self-Regenerating Diesel Exhaust Particulate Filter and Material,” and U.S. Pat. No. 5,758,496, “Particulate and Exhaust Gas Emission Control System.”
DPF technologies, including CDPFs, are generally effective in greatly reducing emissions of PM, but fail to reduce NOx from diesel emissions.
The present applicant's previous patents, U.S. Pat. Nos. 5,085,049 and 5,251,564 teach novel methods of reducing PM, HC, and NOx simultaneously by employing an “active” CDPF system combined with a cooled EGR process. The similar DPF-EGR process, with a “passive” DPF system coupled with hot EGR system, described in U.S. Pat. No. 5,806,308, failed to regenerate the DPF under actual driving conditions. Therefore, an “active” CDPF system, coupled with a cooled EGR system, is needed to guarantee trap regeneration in all driving conditions.
Another method of reducing NOx emissions from diesel engines is to utilize water in the combustion chamber to reduce the peak flame temperature. Water additive methods known in the art include 1) water-injection, 2) water-fuel emulsion, and 3) water-fumigation.
However, water-addition methods including the EGR process are not widely practiced in diesel engine combustion systems, because of concerns about possible engine wear problems caused by the break-down of the protective film of lubricating oil by contact with water in critical rubbing metal surfaces, such as the surfaces between piston rings and cylinder walls and valve bearings, etc. It is, therefore, desirable to develop more effective engine lubricating oil compositions, and lubricating systems that will function better under the presence of water in diesel engine combustion systems.
A lubricant oil composition especially suitable for a pressure-accumulating (common rail) type diesel engine with an EGR system was proposed by U.S. Pat. No. 6,329,328 in which organomolybdenum coumpound, zinc dialkyl dithiophosphate, and Ca or Mg and Zn salts of alkyl salicylate are incorporated with a base oil composed of a mineral and/or synthetic oil.
U.S. Pat. No. 4,946,609 discloses an engine lubricating oil for diesel engines equipped with a DPF in the exhaust gas system, consisting of diesel engine lubricating oil and 5-20,000 ppm, based on said engine lubricating oil, of an iron compounds of ferrocene and/or a ferric salt of tall oil. The use of diesel engine lubricating oil containing iron compounds, as shown in U.S. Pat. No. 4,946,609, is not always sufficient for inducing catalytic regeneration of the collected PM in all driving modes.
Similarly, U.S. Pat. No. 5,386,804 discloses a process for the addition of ferrocene to combustion or motor fuels, using improved metering of the additive into the combustion chamber.
For internal combustion engines such as diesel engines, it is possible to periodically direct controlled amounts of used crankcase oil to the fuel tank, where the used oil mixes with the fuel, and is burned therewith during engine combustion. There are many methods of implementing automatic crankcase oil change and makeup systems, such as those disclosed in as U.S. Pat. Nos. 5,390,762; 4,495,909; 4,421,078; and 4,417,561. However, burning used engine oil in diesel fuel, by the methods disclosed in these patents, emits more air-pollutants, and is not allowed in some countries without use of DPF system.
An improved CDPF system is therefore needed, which would more effectively reduce unwanted pollutants. In particular, a CDPF system is needed which is operable to reduce emissions of both PM and NOx simultaneously.
It would be advantageous if a CDPF system were available which could beneficially improve engine oil lubricity and effectiveness.